Fig. 3. Expression of Cyp1B1 in normal and vitamin A-deficient (VAD) quail embryos. Arrows represent regions where expression of Cyp1B1 is seen in normal embryos but not in the VAD embryos. (Aa) Dorsal view of a normal 10s (HH10) embryo. (Ab,Ac) Equivalent view of a HH10 VAD embryo showing Cyp1B1 expression in the MHB (white arrow), paraxial mesoderm of the hindbrain (blue arrowhead) and all of the somites. Expression is absent from the r2 region as compared with normal embryos (white arrow). (Ba) Cyp1B1 expression in a HH16 embryo and (Bb) in a transverse section in the plane indicated by the white line. (Bc) Dorsal view of 23s VAD quail and (Bd) enlargement of spinal cord region. The location of transverse sections are indicated by black lines. Cyp1B1 is missing from the sinus venosus (red arrow), eye (white arrow) and pharyngeal arch areas (blue arrow). Transverse sections (Be-Bg) reveal that the expression in the notochord (Be, orange arrow) is lost as compared with the normal (Bb, orange arrow). The green arrow in Be indicates mesoderm beside the hindbrain. (Ca-Cc) Sites of altered expression are also observed in a 30s (HH17) VAD embryo compared with its normal counterpart. These include the epiphysis, the eye and heart (Ca compared with Cc, orange, white and pink arrows, respectively). The blue arrows in Ca and Cc indicate loss of expression in the branchial arches. (Da,Db) Rescue of Cyp1B1 expression in the anterior of the embryo and particularly the eye (white arrow) by the exogenous addition of RA.